The long-term objective of this proposal is to gain insight into mechanisms of cutaneous host defense against bacterial skin pathogens. There are an increasing number of studies demonstrating that Toll-like receptors (TLRs) respond to components of bacteria and other microbial pathogens and subsequently initiate innate and adaptive immune responses. Our preliminary data in a mouse model system of Staphylococcus aureus induced skin ulceration suggest that TLRs and TLR signaling molecules are important in cutaneous host defense against bacterial skin infections. We hypothesize that TLRs play a crucial role in initiating innate and adaptive immune responses that are important in controlling bacterial skin infections. We propose experiments to investigate the role of TLRs and TLR related signaling molecules in cutaneous host defense against the most common skin pathogen, Staphylococcus aureus. The ability of TLRs to sense an infection and to generate immune responses such as production of antimicrobial peptides, recruitment immune system cells, and initiation of innate and adaptive immune responses will be investigated. In addition, since cultured keratinocytes and epidermal keratinocytes from human skin specimens have been shown to express TLRs, we will also investigate the functional role that human keratinocytes have in sensing and initiating cutaneous host defense mechanisms against Staphylococcus aureus in culture. We believe the insights obtained from the study of TLRs in bacterial skin infections will help broaden our understanding of cutaneous host defense and allow for much needed novel antibacterial therapies, which may be of particular importance since there are increasing numbers of bacterial strains that are resistant to conventional antibiotic therapy.